While I don't think it's completely ok to wish for Trump's death, I can understand why some react the way they do. Some, at least initially, doubted that he has tested positive at all and that this is just some kind of stunt, which is a bit sad but also a reflection of Trump's presidency. He's told so many lies during his time as president that it's no wonder that people doubt everything he says or does, even if it's something as serious as a Covid-19 infection.
People showing a lack of sympathy also comes as no surprise when you take into consideration just how disrespectful and flat out evil Trump has been during these years. Add his terrible management of the corona crisis, and the numerous tragedies that that has resulted in, to the mix and it's not that hard to understand why some people react the way they do.
